Due to how the fediverse works if users can be given a did so can a community. It would only migrate for services that support did but wouldn't be all to different.
DID already exist they are a Decentralised IDentiy (DID) it is a keypair and user data so usernames, profile, bio, and a list of accounts across different instance that allows associating post comments likes etc.
No thats the whole point of a DID. Its an existing standard that has been established to manage decentralised identity. Their exists multiple ways to handle it so a did is did:source:id where the source can be many different things blue-sky uses a group of trusted identity server, but u can use a selhosted file, the blocckchain all sorts of things. Hell u could even use bluesky u could have the same login for ATproto (bluesky) and activpub (lemmy)
If there is anyone who knows anything it is the insurance companies. Thats their literal job to calculate the risks of something costly with heigh accuracy so they can put a price on it thus distributing a large single cost across many people as a small regular cost. If an insurance company doeant want to do somthing hiatory would tell us there is a damn good reason why.
Yeah that's critical without it everything would break